The present invention relates to ink jet printers, and, more specifically, to a method and apparatus for fixing ink to a print receiving medium.
Ink jet printers typically include recording heads, referred to hereinafter as printheads, that employ transducers which utilize kinetic energy to eject droplets of ink. For example, thermal printheads rapidly heat thin film resistors (or heaters) to boil a liquid-based ink, thereby ejecting a droplet of the ink onto a print receiving medium, such as paper. According to this ink jet method, upon firing a resistor, a current is passed through the resistor to rapidly generate heat. The heat generated by the resistor rapidly boils or nucleates a layer of ink in contact with or in proximity to a surface of the resistor.
The nucleation causes a rapid vaporization of the ink carrier or vehicle, creating a vapor bubble in the layer of ink. The expanding vapor bubble pushes a portion of the remaining ink through an aperture or orifice in a plate, so as to deposit one or more drops of the ink on a print receiving medium, such as a sheet of paper. The properly sequenced ejection of ink from each orifice causes characters or other images to be printed upon the print receiving medium as the printhead is moved relative to the print receiving medium.
Until the ink deposited on a print receiving medium has become fixed thereto, problems such as bleeding, cockling, and smearing can occur, especially when using inks having an aqueous-based carrier, and print receiving media such as plain paper. For example, bleeding can include both lateral bleeding and penetrating bleeding, and is generally caused by the absorption of the carrier into the print receiving medium. Lateral bleeding involves lateral movement of the ink through the print receiving medium (e.g., in paper, spreading across adjacent fibers of the paper). Penetrating bleeding, on the other hand, involves longitudinal movement of the ink through the print receiving medium (e.g., in paper, penetrating towards the back of the paper).
In general, lateral bleeding can reduce the definition of the resultant image. Meanwhile, penetrating bleeding can, for example, reduce optical density and hinder duplex printing. Furthermore, cockling, which also involves the absorption of the carrier into the print receiving medium, can deform the surface of the print receiving medium and induce waviness in the resultant image.
Smearing involves movement of the ink across the surface of the print receiving medium. For example, relative movement between a print receiving medium upon which ink has been deposited, but not fixed, and a second object (e.g., the hand of a user handling the object or another print receiving medium) can cause smearing. Accordingly, it is desirable for the ink deposited on a print receiving medium to be substantially fixed thereto before the user handles the medium and/or before the medium is placed in contact with the next print receiving medium. Therefore, as printing speeds have increased, a throughput limitation for ink jet printers has become the fixation time of the ink.
Conventionally, it is known to use surfactants to reduce the susceptibility of an ink to smearing (as well as reducing the susceptibility of the orifices of the printhead to clogging), but adding surfactants tends to increase the susceptibility of the ink to bleeding. In addition, printing methods, such as shingling methods, where only a fraction of the ink is deposited in each pass of the printhead, have been developed to reduce problems such as bleeding and cockling. Generally, as these methods involve depositing less ink per each pass, these methods typically increase the amount of passes needed, thereby adding additional time to the printing process and slowing the throughput of the printer.
Other attempted solutions to these problems have included exit stackers for separating a print receiving medium with unfixed ink from other print receiving media, and precoating print receiving media to limit the absorption of the carrier. However, these proposed solutions can be costly and may not adequately resolve all of the potential problems. Yet another approach to solving problems such as bleeding, cockling, and smearing has been to incorporate dryer devices within the printers. In some cases, multiple dryer devices have been utilized in the paper path of a printer.
Conventional dryer devices have utilized high temperatures and/or high air speeds to reduce the time required to fix the ink to the print receiving medium. Typically, these dryer devices will utilize powers between 750 to 1000 Watts, often causing the heating mechanisms in the dryer devices to glow orange hot, in an effort to speed the fixation time. As can be understood, because of the high temperatures involved, conventional dryer devices can present both bum and fire safety issues (e.g., when the user is exposed to the dryer device, such as when clearing paper jams or the like). Moreover, these devices are typically relatively large consumers of power, and can be obtrusive in the design of the printer.
Accordingly, it would be advantageous to have an inkjet printer and method for improving the fixation time of ink. It would also be advantageous to have an inkjet printer and method for improving print quality. Moreover, it would be advantageous to have such an inkjet printer and method that consumes relatively less power and reduces burn and/or fire safety issues. Furthermore, it would be desirable to have an inkjet printer and method which utilizes an unobtrusive device to meet these goals.
Accordingly, it is an object of the present invention to provide an inkjet printer and method that overcomes the problems associated with conventional inkjet printers.
It is another object of the present invention to provide an inkjet printer and method for improving the fixation time of a deposited ink.
It is a further object of the present invention to provide an inkjet printer and method for improving print quality.
Still another object of the present invention is to provide such an inkjet printer and method that consumes little power and reduces burn and/or fire safety issues.
Yet a further object of the present invention is to provide an inkjet printer and method which utilizes a tepidity device having an unobtrusive design.
According to one embodiment of the present invention, an inkjet printer assembly comprises a printhead and a tepidity device. The printhead is capable of providing droplets of ink on a portion of a print receiving medium within a print zone. The portion of the print receiving medium within the print zone is at least partially exposed to an atmosphere having a temperature.
Meanwhile, the tepidity device is capable of being in thermal contact with the droplets of ink provided on the portion of the print receiving medium within the print zone. The tepidity device is also capable of generally warming the droplets of ink provided on the portion of the print receiving medium within the print zone to a temperature of up to about 16xc2x0 Celsius above the temperature of the atmosphere to which the print zone is at least partially exposed while the portion is substantially within the print zone. Preferably, the tepidity device is capable of being in conductive thermal contact with the droplets of ink provided on the portion of the print receiving medium.
In preferred ink jet printer assemblies according to this embodiment, the printhead includes a plurality of nozzles capable of ejecting the droplets of ink and the tepidity device generally opposes the nozzles of the printhead. According to another preferred embodiment, the tepidity device is capable of being in direct contact with the portion of the print receiving medium. Preferably, the tepidity device can generally warm the droplets of ink provided on the portion of the print receiving medium by being energized with a power of between about 6 to about 12 Watts. In yet another preferred embodiment of the present invention, the tepidity device is capable of generally warming the droplets of ink to a temperature of between about 40 to about 16xc2x0 Celsius above the temperature of the atmosphere to which the print zone is at least partially exposed. Preferably, the tepidity device comprises an electrothermal converting element.
In another embodiment of the present invention, a method for printing on a print receiving medium includes the step of providing a portion of a print receiving medium in a print zone. The portion of the print receiving medium within the print zone is at least partially exposed to an atmosphere having a temperature. The method also includes providing ink onto selected locations of the portion of the print receiving medium within the print zone. Moreover, the method further includes generally warming the droplets of ink provided on the portion of the print receiving medium within the print zone to a temperature of up to about 16xc2x0 Celsius above the temperature of the atmosphere to which the print zone is at least partially exposed while the portion is substantially within the print zone.
While the step of providing the ink can occur before or after the step of generally warming the droplets of ink, it preferably occurs substantially simultaneously with the step of generally warming the droplets of ink. A preferred embodiment of the present invention can also include the step of placing a tepidity device in thermal contact with the droplets of ink. In such an embodiment, the tepidity device is preferably placed in thermal contact with the portion of the print receiving medium within the print zone. In this embodiment, the tepidity device generally warms the portion of the print receiving medium to generally warm the droplets. In a more preferred embodiment, the method further includes the step of transferring thermal energy from the tepidity device to the portion of the print receiving medium after the step of placing a tepidity device in thermal contact with the portion of the print receiving medium within the print zone.
In a preferred embodiment, the step of generally warming the droplets of ink provided on the portion of the print receiving medium within the print zone also generally warms the droplets of ink to a temperature of between about 4xc2x0 to about 16xc2x0 Celsius above the temperature of the atmosphere to which the print zone is at least partially exposed. In other preferred embodiments, the preferred step of generally warming the portion of the print receiving medium within the print zone warms substantially all of that portion. In yet another preferred embodiment, the step of generally warming the droplets of ink provided on the portion of the print receiving medium within the print zone includes generally warming a tepidity device to a temperature of between about 4xc2x0 to about 16xc2x0 Celsius above the temperature of the atmosphere to which the print zone is at least partially exposed.
Still other aspects of the present invention will become apparent to those skilled in this art from the following description, wherein there is shown and described various embodiments of this invention, simply by way of illustration. As will be realized, the invention is capable of other different aspects and embodiments without departing from the scope of the invention. Accordingly, the drawings and descriptions should be regarded as illustrative in nature and not as restrictive in nature.